Expansion anchors are known generally and used frequently for fastening objects, or fixtures, to a base material by installing the expansion anchor in a pre-drilled hole formed in the base material, which is often concrete, or brick, or mortar, or more generally any material suitable for receiving such an expansion anchor. An anchor known commonly as the Rawl-Bolt.RTM. anchor, for example, includes generally a hex head bolt having an extension sleeve and an expander sleeve separated by a nylon compression ring all disposed and retained about the bolt shaft by an expander cone, or nut. The expander cone is partially disposed about a threaded end portion of the bolt shaft, and an over-sized slotted end portion of the expander cone is compressed by the base material as the Rawl-Bolt.RTM. anchor is driven into the pre-drilled hole so as to prevent rotation of the nut during tightening of the bolt. As torque is applied to tighten the Rawl-Bolt.RTM. anchor, the expander cone is pulled toward the bolt head between the bolt shaft and the expansion sleeve so as to expand the expansion sleeve in the pre-drilled hole thereby engaging the wall of the hole. Further tightening of the Rawl-Bolt.RTM. anchor allegedly advances the threaded portion of the bolt shaft into the compressed end portion of the expander cone so as to subsequently outwardly expand the compressed expander cone, which thereby engages the wall of the pre-drilled hole in the base material. The nylon compression ring is crushed to permit the further tightening of the Rawl-Bolt.RTM. anchor after expansion of the expansion sleeve so as to draw the bolt against the fixture.
The expanded nut portion of the Rawl-Bolt.RTM. anchor, however, provides only limited additional anchoring performance since the compressed portion of the nut can not be expanded any further after the bolt shaft is driven fully through the nut.
Most of the anchoring effect of the Rawl-Bolt.RTM. anchor thus results from the expansion of the expander sleeve. In addition, the nylon compression ring limits the extent to which the bolt can be further advanced into the pre-drilled hole after expanding the expansion sleeve thereby limiting the extent to which the fixture can be clamped against the surface of the base material. Also the location of the nylon compression ring about the shaft the Rawl-Bolt.RTM. anchor has a tendency to adversely affect the shear performance of the Rawl-Bolt.RTM. anchor. More specifically, the nylon compression ring results in a region of shear susceptibility between the upper sleeve and the expansion sleeve since the bolt shaft is not strengthened by either the metal upper sleeve or the metal expansion sleeve in the region of the compression ring.
The Rawl-Bolt.RTM. anchor requires that a nylon plug or other cap member cover an exposed end portion of the expander cone partially disposed about the threaded end portion of the bolt shaft so as to prevent damage to the threaded bore of the expansion cone prior to installation and while the expansion cone is initially driven into the pre-drilled hole. The Rawl-Bolt.RTM. anchor also includes adhesive tape applied partially over the expansion sleeve and the expander cone so as to prevent expansion of the expansion sleeve during shipping and handling prior to installation. The Rawl-Bolt.RTM. anchor is thus a relatively costly product as a result of the fabrication and assembly of its multiple components, including the formation of the slots on the expander cone, which is a particularly costly operation.
In view of the discussion above among other considerations, there exists a demonstrated need for an advancement in the art of expansion anchors and methods therefor.